Laser beam levelling devices serve to establish a horizontal or inclined plane and are used for building purposes. The laser beam issuing from the device is received a certain distance away by a receiver. The inclination of the imaginary plane between the laser beam system and the receiver may therefore be measured. Laser beam levelling devices are used, for example, in excavation and the grading of pits, in the control of concrete foundations and concrete floors, alignment of shuttering, in the levelling of track members for construction cranes and in many other applications.
Conduit construction laser systems are a subgenus of laser beam levelling devices. They are used in the construction of pipelines, for example drainage lines, to lay the individual lengths of pipe in the desired inclination and direction. The lengths of pipe are lined up until they form a pipeline with an inclination of, for example, 1.2%. Shafts are installed at intervals of 50 to 70 m. There is no change of direction between the shafts. The inclination of the individual portions of pipeline between the shafts must be selected so as to differ in each case in practice.
During the construction of a pipeline, the conduit construction laser system is erected at the beginning of a line, i.e. normally in the region of a shaft, such that the laser beam points in the desired direction and has the desired inclination. The laser beam therefore indicates both the direction and the inclination in which the pipeline is to be constructed. A receiver is inserted at the opposite end of the length of pipe to be positioned. The receiver has a transparent plate with markings in the form of a reticle. The laser beam issuing from the conduit construction laser system impinges on the plate of the receiver as a light spot. As soon as this light spot is located in the centre of the reticle, the length of pipe is correctly positioned and may be fastened in this position.
Helium-neon laser tubes producing a laser beam which is visible to a maximum distance of 100 m, depending on the optical system concentrating the laser beam, are installed in formerly known conduit construction laser systems. The light spot is consequently greater at the receiver and is no longer visible. For reasons of cost, pipeline manufacturers increasingly wish to increase the intervals between the individual shafts, for example by omitting every second shaft. The resultant shaft intervals of up to 140 m cannot however be accomplished with former conduit construction laser systems.
So-called laser diodes have also become available recently. These have the advantage that they consume far less power than conventional helium-neon laser tubes. The former conduit construction laser systems are allocated to an external power source owing to the high energy consumption of the laser tubes. Furthermore, laser diodes are considerably smaller in their dimensions so the overall size of the laser systems could be smaller, making them suitable for the construction of smaller diameter pipelines. The former conduit construction laser systems are suitable for pipelines having diameters of at least 150 mm. The drawback is that the laser beam from the formerly offered laser diodes is visible only up to 40 or at most 50 m.